netdev - [PATCH] net: revert default NAPI poll timeout to 2 jiffies

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Message-ID: <158617317267.1170.12944758673162826206.stgit@buzz>
Date:   Mon, 06 Apr 2020 14:39:32 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Dmitry Yakunin <zeil@...dex-team.ru>,
        "David S. Miller" <davem@...emloft.net>,
        Matthew Whitehead <tedheadster@...il.com>
Subject: [PATCH] net: revert default NAPI poll timeout to 2 jiffies

For HZ < 1000 timeout 2000us rounds up to 1 jiffy but expires randomly
because next timer interrupt could come shortly after starting softirq.

For commonly used CONFIG_HZ=1000 nothing changes.

Fixes: 7acf8a1e8a28 ("Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning")
Reported-by: Dmitry Yakunin <zeil@...dex-team.ru>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 net/core/dev.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 9c9e763bfe0e..df8097b8e286 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4140,7 +4140,8 @@ EXPORT_SYMBOL(netdev_max_backlog);
 
 int netdev_tstamp_prequeue __read_mostly = 1;
 int netdev_budget __read_mostly = 300;
-unsigned int __read_mostly netdev_budget_usecs = 2000;
+/* Must be at least 2 jiffes to guarantee 1 jiffy timeout */
+unsigned int __read_mostly netdev_budget_usecs = 2 * USEC_PER_SEC / HZ;
 int weight_p __read_mostly = 64;           /* old backlog weight */
 int dev_weight_rx_bias __read_mostly = 1;  /* bias for backlog weight */
 int dev_weight_tx_bias __read_mostly = 1;  /* bias for output_queue quota */